It is well known that subjecting a person to prolonged periods of inadequate heat dissipation leads to an increase in body temperature (heat stress), indicated by undesirable effects such as discomfort, increased fatigue, decreased physical and intellectual performance and, in extreme cases, death. Body core temperatures in excess of 38° C. will, for example, lead to impaired decision making and increased reaction times whereas core temperatures in excess of 40° C. can cause physiological damage and fatalities. Increased body temperature can result from accumulation of heat from external sources, metabolic processes due to exertion, or a combination of both. Personnel such as fire-crews, “hazmat” operatives such as those working on toxic or generally hazardous cleanup operations, and chemical plant operatives handling hazardous products are potential victims of such heat stress. Such personnel have usually to wear virtually totally sealed garments which severely inhibit cooling effects that would naturally occur due to ambient air flow over the person's skin and clothing.
One possible measure to prevent the onset of heat stress is to blow a cooling gas, usually air, optionally cooled, over the subject's body, which results in cooling of the subject by a combination of convective and evaporative cooling. Studies of heat stress effects have shown that, to minimize such effects, the average desirable amount of cooling supplied to a subject undergoing moderate exertion is a minimum of 100 watts over the area of the torso. (Ref.: “Techniques for Estimating Ventilation Requirements for Personal Air-cooling Systems”, J. W. Kaufman, Naval Air Warfare Center report NAWCADPAX-99-92-TR.)
Various approaches have been proposed to achieve “air-cooling” of subjects. For example, a system disclosed in U.S. Pat. No. 5,243,706 to Frim et al. is one such approach. The construction of the garment disclosed in this reference comprises an air-impermeable layer and an air distribution layer attached together with a corrugated mesh spacer layer in between. A further mesh spacer layer is positioned between the air-permeable layer and the body of the wearer. Cooling air is fed into the space between the air-permeable and air-impermeable layers, exits the air-permeable layer, and is distributed over the body of the wearer. Given the multi-layer construction of the garment and the inclusion of the corrugated spacer layer the flexibility, fit and comfort of the garment would be severely compromised and would be unlikely to meet the desirability criteria defined supra. Also, the relatively high resistance of the mesh fabrics to the flow of air necessitates a high pressure air source not readily available in a portable (or non-tethered) system.
U.S. Pat. No. 5,564,124 to Elsherif et al. discloses a personal ventilation apparatus which comprises a garment incorporating areas of air permeable material, such as open cell foam, to direct air to selected areas of the body. The system also comprises a battery powered blower unit which, optionally, includes thermoelectric heating or cooling devices or filters. Given the small areas over which the cooling air is vented relative to the total area of the torso, the cooling power of the garment disclosed in this reference is likely to be severely limited and not meet the cooling criteria previously defined.
U.S. Pat. No. 5,970,519 to Weber discloses a cooling garment for medical personnel which comprises a simple two-ply construction of an air-impermeable layer and an air-permeable layer, each having minimal thickness, defining a cavity into which air is blown. The cavity has no spacers, or intermediate material or structures except in the shoulder regions to prevent the collapse of the garment in that area when the garment is worn under a heavy apron such as a radiological shield. One distinct shortcoming of such a system is the absence of any intermediate layer to control airflow within the cavity resulting in uneven air distribution. A further shortcoming is the lack of a means for controlling air distribution between the inner air-permeable layer and the body of the wearer. The absence of such mechanisms may cause excessive cooling of some areas of the wearer's body, especially next to the air inlet port, while not supplying sufficient cooling in other areas. It is an objective of the present invention to overcome the shortcomings of the systems described above.